Reloading Scripts Behavior
Every addon uses a register function that allows it to add operators, panels, extra properties etc that it uses to work, it also has an unregister function to undo these changes when the addon is disabled.

If disabling an addon gives errors after being disabled that are related to properties or functions that it setup, then it is a bug in the addon that should be fixed.

You may notice that the addon you refer to is from addons_contrib, which is a collection of addons available that haven't been accepted as official addons to be included in release versions. Chances are this error is a known one and is one of the reasons it is still in contrib. In this case a release candidate is not being considered as a release version and includes the contrib addons, which may not be the best option.

While reloading scripts can help in some cases, it doesn't remove every change and start from scratch, for that you will need to quit then start blender. I believe reloading scripts relies on the unregister functions mentioned earlier to work properly.

Whether you are using a new install or an old one, it depends on the addon scripts enabled to whether any issues like this happen.